She was a 13-year-old schoolgirl and Father Steve was her parish priest. But a friendship that began with trust turned into years of sex abuse, she contends in a lawsuit, with secret encounters in rectories, at parish retreats and in the church confessional.

Now 30, the woman alleges in her complaint that the Rev. Stephen Roszel, pastor of a Catholic parish in Alexandria, convinced her that it was God's will that they carry on the long-term affair. As she finished high school, went off to college and graduated, Roszel allegedly nurtured their relationship through more than 100 letters, and she kept a diary, beginning in the eighth grade.

It was she who finally called it off two years ago, the woman said. By then, she had suffered tremendous stress and anguish, according to her lawsuit.

"I feel it's really essential for me, to heal, to do this," the woman said in an interview. "Otherwise, it's this awful thing that happened to me, and there's nothing I can do about it."

The woman has sued Roszel and the Diocese of Arlington for more than $ 12 million in Alexandria Circuit Court, accusing him of sexual abuse and assault and battery, and the diocese of negligence. Roszel, 42, has been placed on administrative leave by the diocese from his parish, Blessed Sacrament Catholic Church, pending results of the lawsuit and the church's investigation into the matter.

In a statement issued through a lawyer last week, the priest vowed to wage a vigorous defense against the allegations. "I categorically deny any improper activity that would subject me or my church to liability," he wrote. "I have full trust and confidence in the system to know that when all inquiries in this matter are over, that it will be clear that there is no basis to the lawsuit."

Roszel also said in the statement that he had known the woman and her family for many years and that "I deeply regret that our friendship has come to this." He declined further comment on the allegations.

According to the woman's lawsuit, the relationship began when she was a student at the school run by St. Ann's Catholic Church in Arlington. At that time, Roszel, who later moved on to other churches before becoming pastor of Blessed Sacrament in 1990, was 26, and she was 13. At St. Ann's, he frequently worked with youth.

Roszel told her that "a love relationship between the two of them would bring them closer to God," the complaint says. It adds that Roszel told the woman that God was watching over them and that the priest often led them in prayer after sex.

Diocesan officials, who said Bishop John R. Keating first learned of the allegations in November, said they will take action against Roszel if the woman's claims are proved. They released a statement through a lawyer last week that said the alleged sex activities are barred by the church's canon law, the diocese's ethical standards and "the moral law of God."

Although Blessed Sacrament's parishioners have been told that Roszel is on a personal leave, they have not been informed that any allegations are pending against him. He has been gone from the church since November, shortly after lawyer Roger L. Amole Jr. and the woman, named in the lawsuit as Jane Roe, met with diocesan officials to outline their claims.

The lawsuit raises familiar issues for the Catholic Church, which in recent years has struggled with a wave of well-publicized sexual scandals, including the case of James R. Porter, a former priest who was convicted last year of molesting 28 children in Massachusetts during the 1960s and 1970s. Last year, Pope John Paul II acknowledged a need to root out priests who commit such acts.

Lawyers and other specialists estimate that at least 400 priests nationwide have been accused of sexually abusing church members and say that Catholic dioceses have spent about $ 400 million to settle lawsuits filed by victims.

"You find that in a lot of these cases, a priest will tell a victim this is a special relationship sanctioned by God," said Jason Berry, a New Orleans author who spent seven years researching a book on priests and sex abuse. "In many of these twisted alliances, the priest really does fall in love."

In a recent interview at Amole's office, the woman said she decided to sue Roszel because she has realized, through years of therapy, that the relationship was destructive.

"I had started therapy, and I felt angry and frustrated with not having a regular relationship," said the woman, whose name is not being used by The Washington Post because she is a possible victim of sexual abuse.

Among other things, she said, she suffers from depression and post-traumatic stress disorder, has frequent flashbacks and nightmares, and has had difficulties in relationships with men.

The complaint has been under seal since it was filed Dec. 3, under orders from Circuit Court Judge Donald H. Kent. However, lawyers are free to divulge its contents, and Amole recently allowed The Post to review it.

According to the lawsuit, the woman's relationship with the priest is a story of betrayal.

Not long after they met in 1977, Roszel singled out the 13-year-old for special attention, the complaint says. He made suggestive remarks, sent her cards and flowers, and frequently visited her and her family.

Soon after the relationship began, the sexual activity started, she alleges in her suit. The complaint also says that Roszel frequently wrote her letters and includes excerpts from several of them.

One letter from the priest arrived on the girl's 14th birthday, the complaint says. "When I got to St. Ann's I discovered how special you were to me and I love you very much," the letter allegedly said. "I didn't think or worry about it. I enjoyed it and gave thanks to God that you were here."

A second letter from Roszel, dated May 1, 1979, allegedly included the statements, "I'm still God's message to you that you are lovable, good and beautiful. Not to mention soft tender and pretty."

Another letter, written nine years later, according to the complaint, said: "As scary as things are I thank God every day for you in my life. You are pretty and sexy."

The complaint also said the teenager kept a diary of the affair with Father Steve. "I'm slowly but quickly going nuts! Help! Physically I feel strange," the girl wrote on Nov. 16, 1978. "Why can't I go to sleep. . . . Steve -- so hard just to give him my love and no future."

In another diary entry, dated Nov. 7, 1979, and addressed "Dear Jesus," the 15-year-old allegedly wrote, "I love being close to him -- yet I feel as though that helps us become closer in a way in which we're not meant to."

The complaint says the relationship continued as Roszel moved from St. Ann's to other churches, including assignments at Our Lady of Lourdes in Arlington, St. Philip's in Falls Church, St. Mary's in Alexandria and Blessed Sacrament. Roszel occasionally pulled away from the relationship for short periods, the woman claims in her suit.

The lawsuit also alleges that other priests knew of the affair and that the diocese should have taken action against Roszel long ago.

"I feel like I'm a spiritual person, but I'm having a lot of problems with the Catholic Church," the woman said. "I can't go to church without having an anxiety attack. I just really feel betrayed by them."